The Collaborative International Dictionary of English v.0.48:

Discoloration \Dis*col`or*a"tion\, n. [Cf. F. decoloration.]
   1. The act of discoloring, or the state of being discolored;
      alteration of hue or appearance. --Darwin.
      [1913 Webster]

   2. A discolored spot; a stain. --Arbuthnot.
      [1913 Webster]

WordNet (r) 3.0 (2006):

discoloration
    n 1: a soiled or discolored appearance; "the wine left a dark
         stain" [syn: stain, discoloration, discolouration]
    2: the act of changing the natural color of something by making
       it duller or dingier or unnatural or faded [syn:
       discoloration, discolouration]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "discoloration":
   achromatization, birthmark, blanching, blaze, bleach, bleaching,
   blemish, blotch, brand, bruise, caste mark, check, checkmark,
   cicatrix, cut, dapple, decoloration, decolorization, decolorizing,
   discolor, discolorment, dot, earmark, engraving, etiolation,
   fading, fleck, flick, freckle, gash, graving, hack, jot, lentigo,
   lightening, macula, madder bleach, mark, market bleach, marking,
   mole, mottle, nevus, nick, notch, paling, patch, point, polka dot,
   prick, puncture, scar, scarification, score, scotch, scratch,
   scratching, speck, speckle, splash, splotch, spot, stain, stigma,
   strawberry mark, tattoo, tattoo mark, tick, tittle, watermark,
   whitening